RE: [PATCH v3 01/13] mfd: Add i.MX generic mix support

[Aisheng Dong]

> From: Abel Vesa <abel.vesa@xxxxxxx>
> Sent: Thursday, April 30, 2020 6:04 PM
> To: Lee Jones <lee.jones@xxxxxxxxxx>
> On 20-04-24 07:27:27, Lee Jones wrote:
> > On Thu, 23 Apr 2020, Aisheng Dong wrote:
> >
> > > > From: Abel Vesa <abel.vesa@xxxxxxx>
> > > > Sent: Wednesday, April 22, 2020 5:19 PM On 20-04-17 09:07:47, Lee
> > > > Jones wrote:
> > > > > On Wed, 15 Apr 2020, Abel Vesa wrote:
> > > > >
> > > > > > Some of the i.MX SoCs have a IP for interfacing the dedicated
> > > > > > IPs with clocks, resets and interrupts, plus some other specific control
> registers.
> > > > > > To allow the functionality to be split between drivers, this
> > > > > > MFD driver is added that has only two purposes: register the
> > > > > > devices and map the entire register addresses. Everything else
> > > > > > is left to the dedicated drivers that will bind to the registered devices.
> > > > > >
> > > > > > Signed-off-by: Abel Vesa <abel.vesa@xxxxxxx>
> > > > > > ---
> > > > > >  drivers/mfd/Kconfig   | 11 +++++++++++
> > > > > >  drivers/mfd/Makefile  |  1 +
> > > > > >  drivers/mfd/imx-mix.c | 48
> > > > > > ++++++++++++++++++++++++++++++++++++++++++++++++
> > > > > >  3 files changed, 60 insertions(+)  create mode 100644
> > > > > > drivers/mfd/imx-mix.c
> > > > >
> > > > > For completeness - Arnd's reply to this patch:
> > > > >
> > > >
> > > > I'm replying here to Arnd's reply.
> > > >
> > > > I'm trying to give here a whole picture of the entire problem
> > > > while the documentation for i.MX8MP is _not yet_ public.
> > > >
> > > > Historically, each IP would have its own enclosure for all the related GPRs.
> > > > Starting with i.MX8MP some GPRs (and some subparts) from the IP
> > > > were placed inside these mixes.
> > > >
> > > > Audiomix for example, has multiple SAIs, a PLL, and some reset
> > > > bits for EARC and some GPRs for AudioDSP. This means that i.MX8MP
> > > > has 7 SAIs, 1 EARC and
> > > > 1 AudioDSP.
> > > > Future platforms might have different numbers of SAIs, EARCs or
> AudioDSPs.
> > > > The PLL can't be placed in one of those SAIs and it was placed in audiomix.
> > > > The i.MX8MP has at least 4 of these mixes.
> > > >
> > > > Now, the commonalities between all mixes are:
> > > >  - have their own power domains
> > > >  - driven by dedicated clock slice
> > > >  - contain clocks and resets
> > > >  - some very subsystem specific GPRs
> > > >
> > > > Knowing that each mix has its own power domain, AFAICT, it needs
> > > > to be registered as a single device. Considering that it can have
> > > > clocks (audiomix has gates, muxes and plls), I believe that needs
> > > > a clock driver, even more so since the muxes need their parents
> > > > from the platform clock driver. Same principle applies to reset
> > > > bits. The subsystem specific GPRs can be registered as syscon
> > > > devices and taken care of by its counterpart IP (e.g. the AudioDSP specific
> regs would be taken care of by the DSP driver, if there is one).
> > > >
> > > > Now based on all of the above, by using MFD we take care of the
> > > > power domain control for the entire mix, plus, the MFD doesn't
> > > > have any kind of functionality by its own, relying on its children
> > > > devices that are populated based on what is in the mix MFD devicetree
> node.
> > > >
> > >
> > > How about doing like this which maybe can address Arnd's concerns?
> > > audiomix: audiomix@30e20000 {
> > >         compatible = "fsl,imx8mp-audiomix", "syscon";
> > >         reg = <0x30e20000 xxx>,
> > >               <0x30e20xxx xxx>;
> > >         reg-names = "audio", "reset", "...";
> > >         #clock-cells = <1>;
> > >         #reset-cells = <1>;
> > >         power-domains = <&audiomix_pd>; }
> > >
> > > That means we have one combo driver registering two controllers
> > > (clk/reset), both use the same power domain as audiomix.
> > > And it can be easily extended to support more services provided by
> > > audiomix over syscon if needed.
> > > Then the 'dummy' MDF driver is not needed anymore.
> > >
> > > Jones & Arnd,
> > > How do you think?
> >
> > Sounds okay in principle.  Anything that prevents the existence of a
> > dummy (a.k.a. pointless) MFD must be seen as a positive move.
> >
> 
> OK, I'll do it in a single driver and single dts node.
> 
> But there might be an issue with the placement of this new driver.
> 
> drivers/clk/imx/ could be an option, but the driver will use a lot of different APIs
> from different subsystems. Not the audiomix, but the future mixes.

Maybe Stephen could comment whether it's ok to push a combo driver
(e.g. clk&reset&syscon) In drivers/clk/imx.

From what we see, it seems already some similar combo drivers (clk&reset) there.

BTW, not sure if any technical block reasons to put in drivers/clk.
Maybe we can quickly try internally first.

Regards
Aisheng

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